U.S. Pat. No. 3,913,766 discloses a storage and retrieval crane system that includes a tower having a pair of spaced columns and a tower drive for moving the tower horizontally along rails on a floor between storage racks. A carriage is coupled to a carriage drive mounted on the tower for vertical movement between the columns. A shuttle table is carried by a telescoping by-directional assembly on the carriage, and is coupled to a shuttle drive mechanism for moving the shuttle horizontally from the carriage in directions lateral to the direction of movement of the tower along the floor. By control of motion of the tower along the floor, the carriage on the tower and the shuttle on the carriage, parts are selectively stored in and retrieved from storage racks that extend along opposite sides of the tower rails.
A basic problem in storage and retrieval systems and methods of this character lies in potential malfunction or failure of any one of the drive mechanisms, which in turn causes the entire crane to be taken out of service. It is a general object of the present invention to provide a storage and retrieval system and method that will reduce or eliminate down-time associated with drive system failure in the prior art.
A storage and retrieval crane system in accordance with a presently preferred embodiment of the invention comprises a tower having a pair of spaced columns and a tower drive mechanism for moving the tower horizontally along a floor between storage racks. A carriage is coupled to a carriage drive mechanism for vertical movement between the columns, and a shuttle is coupled to a shuttle drive mechanism on the carriage for moving the shuttle horizontally from the carriage in directions lateral to direction of movement of the tower along the floor. At least one of the drive mechanisms, and preferably all of the drive mechanisms, include primary and secondary drive arrangements, and facility for selectively alternately connecting one or the other of the primary and secondary drive arrangements to drive the tower, carriage or shuttle. Thus, in the preferred embodiment of the invention, each of the drive mechanisms is fully redundant, so that machine drive may be switched from primary to secondary mechanisms in the event of failure without significant down-time or loss of production.